Conventionally, many injection holes are provided on a wall surface such as a rotor blade in a gas turbine engine (hereinafter simply referred to as “gas turbine”) such that they are oriented in the same direction. A film flow of a cooling medium such as air injected from these injection holes cools the wall surface exposed to high-temperature gas. As such a film cooling structure, for example, it is proposed that a rib having a substantially isosceles triangle shape in a plan view, having a base at a rear end of each of the injections holes and a vertex positioned at an upstream side (front side), is provided at a center portion of an injection port through which the cooling medium is injected to the wall surface, and is configured to disperse the cooling medium to the right and to the left, thereby cooling the wall surface uniformly (Patent Literature 1).